In this project, we learn how to create a high range FM transmitter, which has the range of 2 kilo meter (2KM) radius. This is basically a simple DIY hobby circuit and you can try it in your home with minimal components. Start building this high range FM transmitter and see how your output comes.

Description.
With a matching antenna, the FM transmitter circuit shown here can transmit signals up to a range of 2 kilo meters. The transistor Q1 and Q2 forms a classic high sensitive preamplifier stage. The audio signal to be transmitted is coupled to the base of Q1 through capacitor C2. R1, R3, R4, R6, R5 and R9 are the biasing resistors for the preamplifier stage comprising of Q1 and Q2. Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier.C9 and L1 forms the tank circuit which is essential for creating oscillations. Inductor L2 couples the FM signal to the antenna.

Circuit diagram.

Notes.

Assemble the circuit on a good quality PCB.

The circuit can be powered from anything between 9 to 24V DC.

Inductor L3 can be a VK220J type RFC.

For L1 make 3 turns of 1mm enamelled copper wire on a 10mm diameter plastic former. On the same core make 2 turns of 1 mm enamelled copper wire close to L1 and that will be L2.

Hi, I am really excited reading all the comments and the answers from the instructor of the circuit above. With this I have been able to construct this transmitter for my final year project. I was thus having constraints especially getting the components. Now that I have constructed the circuit, I am having a problem regarding the antenna design. can you please help.

Dear sir,
can i make a RF remote controller by using this arrangement.please tell me how ? i have made 4 channel RF remote controller by using ask RF modules and ht12d and ht 12e .but its range is low about 60 meter please tell me how can i increase the range of this controller.
thank you

I want to control the RC Plane by transmitting Encoded signals from H12E via this 2km range transmitter published by John, can I use the same circuit or else do I need to modify the circuit ?
Please guide me incase circuit changes are required ?

Sir seetharanam can you pls tell me how use a unipolar antenna with l2,I couldn’t get a hold of dipole or bipole antenna.and I use 0-40uf for c8 and c9 I dnt knw if it wll do the work.pls reply quickly

i have build a very similar transmitter kit with the metalic 2N2219
Lastly i tried it with about 24 volt and it became really hot.
You must use heatsink with higher than 15 v
The last point i could have measured was about 2,5 km with point to point eye view.
Highly recommened type of circuit, because of the efford to success ratio.
good luck to all …

I want to verify the output of this circuit using the fm receiver built in our mobiles ( Since the frequency is between 88 and 108). How to determine the central frequency of the transmitter so that i can tune the radio to that particular frequency and verify??

Sir if we give the encoded signal from RX600E to the transmitter it will be transmitted or not
Then by using a FM receiver we can encode it or not
By using this I decided to construct a long range remote controlGowthamraj02031996@gmail.com

Sir if we give the encoded signal from RX600E to the transmitter it will be transmitted or not
Then by using a FM receiver we can encode it or not
By using this I decided to construct a long range remote control

Dear Seetharaman, I built this circuit first on a breadboard for testing and it just worked fine. So I assembled it on a piece of general purpose PCB, and it performed just better. For the RF choke I used a choke inductor of 220 uH, I don’t know how to call it officialy, but it looks like an electrolytic capacitor with radial wiring (leads out of the bottom).
For antenna I used a car whip antanna of approximately 1 m (app. 3 ft 4 inch).

I didn’t dare to power this circuit up because of the relatively big transmitting distance (I don’t want law enforcement on my doorstep because I try to learn how radio works:P). But thankfully it performs below the stated 2 km in my assembly. I measured the amount of needed curent and it turned out to be 115 mA, with a lab powersupply of 13.8 V, therefore I rate the power P=13.8*0.115=1.6 W. Note that this isn’t the transmitting power but the power that is needed to operate, transmitting power depends on the type of antenna (please refer to the literature on RF electronics for the complete details)
Because Q3 (a good old metal case 2N2219 tor) gets bloody hot, I just bought myself a 4 cm fan which is to be installed after my schoolday.

I’d like to thank Seetharaman for his nice circuit, it works fine and it’s easy for people who built multiple circuits before this (like myself). If you are an absolute beginner, skip this project, get familiar with transistors in simpler applications, then return an build this amazing circuit.

I want to verify the output of this circuit using the fm receiver built in our mobiles ( Since the frequency is between 88 and 108). How to determine the central frequency of the transmitter so that i can tune the radio to that particular frequency and verify??

Dear All
I have made this circuit before and it work well to 70 m
but in analysing the circuit how Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier?
the third stage is only bandPass amplifier first order
i ,d like to discuss this point

Hello everybody!
I am Social Science graduate of Business Management. but i have special interest to build simple FM transmitter at home. but as i told you i do not have the basic knowledge. but i tried to read so many websites about how to build simple FM radio transmitter and i got some hints but not the basic one.

I got difficulties to get answers related to the following questions.

1, How can i know the voltage of parts used in any homemade FM transmitter? How can i get the exact voltage of parts used in any homemade FM transmitter? I mean how can i determine the voltage of parts used in any homemade FM transmitter? Is there any calculation used/applied to get the voltage of parts used.

(For example, what are the voltage of each parts used in the above FM transmitter?)

Hello Tesfae:
This 2KM FM Transmitter works on low voltage; thus, all of its associated components will do too. However, I am providing you with some hints in this scenario: All the resistors within the schematic will be required to dissipate less than 1/2 Watt, so you should buy at least 1/2 Watt power dissipation resistors; If you plan to plug your transmitter to a +24 VDC source, then you should use 36 VDC rated electrolytic capacitors (C1 and C4), otherwise, 24 VDC rated will do; C3 and C5, being Mylar or Polystyrene capacitors, they should be rated at 50 VDC which is a standard voltage value for these types of components; C6 and C7 “MUST BE CERAMIC CAPACITORS”… I insist… Ceramic Capacitors, and as such, they are normally rated between 500 VDC to 1 KV; last, but not least, we have C8 and C9… variable capacitors come in all shapes and forms, so their final voltage rating will be a function of your preferences. If you buy air- capacitors like the ones furnished in old radios, they can withstand several hundred volts between their plates, if you buy printed-circuit-board-mountable capacitors, they are often times rated at 50 VDC, so as you can see, the standard voltage rating for these components will have you covered. This is a fun project to build and it works just great; nevertheless, you should take into account that temperature changes will make the transmitter´s central frequency to drift back and forth. These variations in your transmitter´s central frequency will create annoying hissing noises in your FM receiver and chances are that you will lose fragments of information every now and then. If you plan to power this unit on batteries alone, you will experience frequency drifting as the batteries begin to become depleted. If you plan to power this transmitter on a fixed power supply, chances are that you will end up changing the transmitter´s output capacitance and your final transmission frequency will need some fine tuning. If this is your case (powering the transmitter from a fixed power supply), and before even striving to use C8 and C9 as your tuning devices, consider widening or stretching L1, L2 and/or L3 coils first, of course, affecting one piece at a time. Although this is a trial-and-error approach, without an RF meter or spectrum analyzer, your ears, an FM receiver, and your fingertips are all you got to succeed in making this extraordinary FM transmitter work. May I wish you the best of lucks and the best of funs while working on this amazing project… enjoy yourself to the bones!

Does this circuit do actual FM transmission (Frequency Modulated Transmission) or else does it just amplify the amplitude of the input signal? I don’t see how it can do frequency modulation as it doesn’t have a carrier signal. Forgive me if I’m wrong.

It is an actual FM Transmitter! Q3, along with its associated components, comprise the transmitter´s oscillation stage. Then, the sound frequencies coming from Q1 (voltage amplification) and Q2 (current source and impedance isolation) through R9 and C5, are algebraically added to the transmitter´s central frequency. The circuit works outstandingly well for a transmitter this size and caliber!

Which is correct process for designing L3?
Seetharaman
April 3, 2014 at 2:27 am
L1 and L2 will be with 18SWG super enameled copper wire and for L3 use 28 SWG 250 turns on 6mm former 5mm width honeycomb winding.
or
seetharaman
August 23, 2013 at 4:12 am

Hi Naren you can use any RH Choke in this place. you can wind around 24 turns of 22swg enemelled copper close wound on 6mm dia self supporting, without any core material(air core)you can wind on a pencil slideout and use.

You can calculate its size according to the transmitter´s wavelength. Let us say that for instance your transmitter’s central frequency if 91.5 MHz (you can find this on the FM receiver you plan to use to receive whatever information you are transmitting with this device), Calculate its wavelength in meters.

3.28 meters would be the perfect antenna size for this frequency; however, any multiple and submultiple of 3.28 will also work perfectly (6.56m, 1.64m, 82cm, 41cm, 20.5cm, and even a 10.25cm-long antenna would work just fine). For practical reasons a too-large or too-short antenna should be discarded, and maybe a 20.5cm long antenna will work just fine for you (believe it or not, it will work), but remember that only 20.5cm equals to 20.5cm. If you use a 20cm long antenna instead, it will not work as well as the original measured at 20.5cm because of a radio frequency transmission phenomena known as “Band Reject”. Remember that you are transmitting through this antenna, and if your antenna is shorter or larger than the transmitter´s frequency wavelength, it will not only transmit but receive radio frequency signals coming from itself. These “received” signals coming from within, will interfere with the signal you are striving to transmit and you will not transmit 100% of the energy generated by the output transistor (in this case Q3).

Yes, name it directional antenna. You can increase the range by directional antennas at each extreme: transmitter and receiver. This is the best aproach, however on one extreme only ( transmitter or receiver) is a good improvement. Albert, from Uruguay, South America.

Sir i completed the circuit..and I have problem when i am going to touch inductor (L1) with my hands at the time i get the output with clear sound…when i released my hands i get only noisy output…..pls pls help me to get clear sound..

Any choke will do. L3 is used only as a filter so radio frequency waves coming from Q3 do not reach the preamplifying transistors. Use the coil of a 24 Volt relay and it will work just fine! Best of luck with your project!

Carbon film
A carbon film is deposited on an insulating substrate, and a helix cut in it to create a long,
narrow resistive path. Varying shapes, coupled with the resistivity of amorphous carbon can
provide a variety of resistances. Carbon film resistors are available in a power rating range of
0.125 W to 3 W at 70 °C. Resistances available range from 1 Ohm to 10 MegOhm. The
carbon film resistor has an operating temperature range of -55 °C to 155 °C. Maximum
working voltages from 200 to 600 Volt DC. Due to the spiral cut nature of the resistance
element Carbon Film Resistors are not suitable for use in radio frequency circuits as they
exhibit high internal inductance.

i have searched L3(VK220J type RFC) for more than 2 months in many shop but i didnt found.. i think its very rear, can you suggest me that where i can find it.. or can we make it by simply turning piece of wire like L1 and L2.. plz give me best advice anyone.

Hi, I’ve have made the circuit but it is not working and I have a suspicion that its either the transistor or the variable capacitors.

For Q3, I couldn’t find the exact transistor, so I switched the 2N2219 for the BC337 NPN Transistor. Problem is, it gets so hot that I can’t touch it, though it doesn’t smoke or burn or anything. Do you think there is a problem here?

Also, where did you buy capacitors for C8 and C9? If you bought it online could you please give me the link? The ones I bought are so dodgy.

PS: I’m doing my major project for the HSC and this is very important for me.
Thank you in advance.

I rebuild this circuit. Very high power output, medium sound quality, super sensitive amplifier and less parts: I like it! Tip: Use cooling for Q3 (someting like a small metall strip,… Dipol antenna works best for this!

Hi there! Im not the admin here, but I guess U can use a dipole antenna for frequency around 100MHz. Take a long pipe of wood/ plasic. Cut two copper wires with a lenght around 75cm. Then attach them to the pipe, so all in all the lenght should be 150cm. Solder the inner ends to a coaxial cable, one to the coat, and one to the core. Then solder a antenna plug,… to the other ends. It should look like this: ~| (~=cable; |= stick with copper wire) If you need more info, google “dipole antenna”

Hello Sir, is this circuit has really more than 1 km range with good quality sound and very low noise?i tried many different 2km FM transmitter circuit on internet but all of those can not go even 150 meter and also full of noise.so i am afraid.PLEASE HELP ME TO INFORM ME ABOUT THIS CIRCUIT…

Hell sir, how making the 2km fm transmiter and this circut in whiche components are used , they components availebal in which city on shope plz list of components and designe the circuit send the data in pdf format

Hi Naren you can use any RH Choke in this place. you can wind around 24 turns of 22swg enemelled copper close wound on 6mm dia self supporting, without any core material(air core)you can wind on a pencil slideout and use.

SIR I AM LAXMAN I WANT MAKE A 2KM FM TRANSMITTER . I HAVE SEEN THE CIRCUIT BUT I AM NOT UNDERSTAND WHAT IS L3 THIS IS A COIL AND WHAT IS C9 40PF AND C815PF .THESE ARE PRE SET THIS IS AVALIABLE IN MARKET AND WHAT IS CALL IN MARKET .

The negative of the supply should be connected to common line shown as connected to ground. All your components are ok except choke. See my earlier comment.
(Hi venkatesh it is an rf choke to prevent rf entering the audio amp stage through power supply. any choke around 200 to 500uH will do. it is normally aircored with 200 to 300 turns honey comb winding to 5mm width with an ID of 6 to 10mm.)

hi i am BetaRajab,
i appreciate the circuit..i really like the range
my problem is i cant find some of the components to finish my projects.
these are..
capacitors- 1000pF,0.033uF,0.022uF,15uF,40pF(trimmer)
transistor-2N2219..
also the type of antenna to be used.

can you help with the voltages of each component..and if possible the equivalent components of each mentioned above in case i cant find them in my area..

I have successfully made the transmitter and I want to say a big thank you to you….. I now want another help from you in making a long distance (above 3km in distance)…. Please help me send the detail to my e-mail address…. salami_azeez0619@yahoo.com …… Please

Plz tell me! spose I have made a very basic FM TRANSMITTER having a 100 meter of rang. Now my question is that is every Fm radio receiver can recieve my voice, witch is transmitted by my FM TRANSMITTER at this rang.

Plz tell me! spose I have made a very basic FM TRANSMITTER having a 100 meter of rang. Now my question is that is every Fm radio receiver can recieve my voice, witch is transmitted by my FM TRANSMITTER at this rang. Reply me! ahsan_mehmood21@yahoo.com

The reason they are adjustable is because according to tolerance differences in ALL of the components you will need to fine tune these two to get the frequency you want. The best way to get the frequency you want is to attach an easily identifiable audio source and set your receiver to the desired frequency. Adjust c9 until you start receiving.

mazhar
Hi Sir ….
My rikavayamenta f. M the transmitter and 2 from
5 km’s and Anne F.M phikvensi. radio
The phikvensi should be separate from …
Do you have a circuit that I receive phikvensi of the person
I’m just so it can be heard …
About 500 to 700 homes in the
I speak only of which can be heard in the house …
mazhar f sathliya-gujarat-dahod-+919227100786

first of all i would like to thanx 4 ua various circuit that help us to learn more electronic knowledges.
i expect to build about 50m fm transmitter of few components, kindly help please,,,,,,,,,,,
by faustine from Dar es salaam Institute of Technology (DIT)

Sir, where I going to connect the L2 terminals/antenna to the circuit diagram? please reply, I am very much excited to create this project, Thank you… please reply to my email address: roygee30@yahoo.com.